The present invention relates to mobile satellite communication terminals for use in a mobile satellite communications system and more particularly, to a mobile satellite communication terminal which can be used not only outdoors but also indoors.
A prior art mobile satellite communication terminal will be explained referring to FIG. 1 showing a diagram for explaining a schematic arrangement of the mobile satellite communications system. The system includes a central earth station 1, a plurality of mobile satellite communication terminals 40-1, 40-2 and 40-3 (which will be sometimes referred to merely as "terminals", hereinafter), and a satellite 2.
More in detail, the terminals 40-1 to 40-3 comprise mobile satellite communication terminals all having the same arrangements and easily portable.
In the illustrated example, one 40-1, e.g., of these terminals 40-1 to 40-3, which is used outdoors, is connected to the central earth station 1 through the satellite 2. In this case, even when moved in between mountains or buildings, the terminal 40-1 can communicate with the central earth station 1 so long as the terminal 40-1 is located within such a range that the terminal can get an unobstructed view of the satellite 2.
In the illustrated example, the terminal 40-2 is installed within such a structure as a building. In this case, when the terminal 40-2 is mounted, e.g., at such a location as in the vicinity of a window 21 that the terminal can get an unobstructed view of the satellite inside of the structure, the terminal can communicate with the central earth station 1 because the attenuation of electromagnetic wave signal caused by the structure is as small as negligible.
Meanwhile, since the terminal 40-3 is positioned at such a location away from the window 21 inside the structure, the terminal cannot get a unbroken view of the satellite 2, the terminal 40-3 cannot transmit send/receive signals with respect to the satellite for the satellite communication.
For the purpose of enabling the terminal 40-3 to attain its communication with the central earth station 1, it is required for the terminal 40-1 to be moved to such a location as in the vicinity of the window that the terminal can receive electromagnetic waves from the satellite as in the case of the terminal 40-2.
As mentioned above, in the prior art mobile satellite communications system, when there is an obstruction which blocks a spatial communication channel or link between the mobile satellite communication terminal and satellite, the communication therebetween becomes impossible. In particular, inside of such a structure as a building, such communication can be established only at such a limited location as in the vicinity of a window.
Thus, even when the mobile satellite communication terminal is of a mobile type, there is a problem that it is impossible to use the terminal with a high flexibility.
An example of the aforementioned mobile satellite communications system is disclosed in a literature, PTC's 93 Proceedings, pp. 835-840, entitled "INMARSAT-M PORTABLE MES."